The present invention relates to high-quality polyurethane (PU) elastomers and polyurethane urea elastomers which exhibit unique combinations of processing characteristics, oxidation resistance, mechanical and mechanical/dynamic properties in particularly demanding applications. These polyurethane elastomers and polyurethane urea elastomers are based on novel polycarbonate polyols.
Polyurethane elastomers were first sold commercially over 60 years ago by Bayer MaterialScience AG under the trade name Vulkollan®, based on 1,5-naphthalene diisocyanate (NDI, which is commercially available from Bayer MaterialScience AG), a long-chain polyester polyol and a short-chain alkanediol.
In addition to polyester polyols, polyether polyols, polycarbonate polyols and polyether ester polyols are also used as long-chain polyols. The choice of long-chain polyol is determined primarily by the requirements of the individual application. The concept of “customised properties” is also used in this connection. For example, polyether polyols are used if hydrolysis resistance and low-temperature properties are a priority. Polyester polyols have advantages over polyether polyols in terms of mechanical properties and UV stability. However, their low microbe resistance is a disadvantage. Polycarbonate polyols combine to some extent the advantages of polyether polyols and polyester polyols, but they are relatively expensive in comparison.
The advantages of polycarbonate polyols lie in particular in their UV stability, hydrolysis resistance and their mechanical properties.
The disadvantage of polyester polyols and polycarbonate polyols and their mixed types, polyester carbonate polyols, as compared with polyether polyols lies in their generally less advantageous low-temperature characteristics. This is due to structural factors and is based on the elevated polarity of carbonyl groups, which normally means that polyester polyols and polycarbonate polyols are partially crystalline, whereas polyether polyols, especially the propylene oxide-based types as the commercially largest group, are amorphous. For partially crystalline systems the relation between glass transition temperature (Tg) and melt temperature (Tm) is described by the known empirical rule established by Beaman and Bayer (M. D. Lechner, K. Gehrke and E. H. Nordmeier, Makromolekulare Chemie, Birkhäuser Verlag 1993, page 327)Tg=2/3Tm  (I)
For example, if polycarbonate polyols have melt temperatures for the partially crystalline components of around 70° C. (343° K), the glass transition temperatures of the amorphous regions are in the order of magnitude of −43° C. (230° K). These values largely also apply if the polycarbonate polyols are present as soft segment polyols in segmented multi-block copolyurethanes, e.g. in the form of thermoplastic polyurethane elastomers (TPU) or polyurethane cast elastomers in integrated form. It is clear from this that it is desirable to have polycarbonate polyols which have a melting range as low as possible. On the one hand, this simplifies processing, and on the other, the working temperature range is extended down to lower temperatures as a consequence of the glass transition temperature, which is likewise reduced.
The upper limit of the working temperature range is determined by the thermal properties of the rigid segments (e.g. urethane, urea, isocyanurate groups, etc.), i.e. the structural elements present in the polyisocyanate building blocks.
The disadvantage of using 1,6-hexanediol as the diol component for polycarbonate polyols or polyadipate polyols, for example, as used in polyurethane chemistry, is the elevated viscosity with otherwise identical characteristic values (molecular weight and functionality).
There have been a number of attempts to modify the melting range of hexanediol polycarbonate polyol, which in industry is the most important polycarbonate polyol for polyurethane elastomers, in such a way as to cover the specific requirements of as many applications as possible. For example, in DE-A 3717060 part of the hexanediol is replaced by hexanediol ether units, for example, leading to a reduced crystalline proportion as compared with pure hexanediol polycarbonate polyol and a melting range shifted to lower temperatures. The disadvantage of this process, however, is that the incorporation of ether groupings has a negative influence on the oxidation and heat ageing resistance, as a result of which some important applications are not viable.
H. Tanaka and M. Kunimura (Polymer Engineering and Science, vol. 42, no. 6, page 1333 (2002)) indicate a way of eliminating at least the aforementioned disadvantage by using 1,6-hexanediol and 1,12-dodecanediol to produce copolycarbonate polyols which have markedly lower melt temperatures than their homopolycarbonate polyols. With the aid of the measurement technique they were using, they measured the melting point of hexanediol polycarbonate polyol at 47.4° C. and that of 1,12-dodecane polycarbonate polyol at 65.5° C., whereas a copolycarbonate polyol with a composition of 70 parts by weight of hexanediol to 30 parts by weight of 1,12-dodecanediol melts at 29.1° C.; this represents a lowering of the melting range by 18.3° C. and 36.3° C., respectively, as compared with the homopolymers. The values for the heat of fusion [J/g] behave in a similar manner, displaying a minimum when the polycarbonate polyol consists of 70 parts of hexanediol and 30 parts of 1,12-dodecanediol.
In spite of these in principle promising approaches, which incidentally were also used on thermoplastic polyurethane elastomers synthesised therefrom, it has so far not been possible to implement this method on an industrial scale, or at least not to any significant extent.
A substantial reason for this is that 1,12-dodecanediol in particular is so expensive that the resulting price of the polycarbonate polyol or copolycarbonate polyol and hence ultimately of the polyurethane elastomer is so high that the advantages that might arise from using 1,12-dodecanediol in whole or in part are outweighed.
This means that any technical advantages would be achieved at too high a cost.
Therefore, an object of the present application was to provide polyurethanes which do not have the aforementioned disadvantages.